In the past, various different schemes are believed to have been utilized in an attempt to flow air through a contained space of a system including an apparatus for conditioning the temperature of the air with the rate of such air flow being related to the static pressure associated with such system. Both the speed and torque of an electric motor in the apparatus and operable generally for driving a fan or blower of the apparatus to effect the air flow through the system are affected by the static pressure thereof, and the rate of air flow (CFM - cubic feet per minute) through the apparatus also affects the motor speed and torque. Thus, if the motor speed and torque were ascertained, the fan manufacturer's data then permitted the calculation of both the flow rate and the static pressure. Motor speed or torque by itself was not enough to determine flow rate or static pressure if the other was not known. In view of the foregoing, it is believed that one of the undesirable features of the aforementioned past apparatus involved rather laborious and time consuming attempts to match motor speed and torque with the proper fan to at least approximate the desired air flow rate for the particular contained space and static pressure of the particular past apparatus or the system in which such apparatus was employed.
Even if the aforementioned match of motor speed and torque with the proper fan might have been made thereby to attain the desired air flow rate for the contained space and static pressure of the past apparatus or system in which it was employed, such static pressure may have been altered during the operation of such system. For instance, it is believed that the opening, closing or mere adjustment of a vent or the like connecting a conditioned space in air flow relation with the system affected the static pressure thereof. Therefore, it is believed that another of the disadvantageous or undesirable features of the past apparatus was that it was unable to accommodate variations in the static pressure thereof in the system in which the past apparatus was employed.
In this vein, if the blower utilized in the past system was of the fan or blade type, a decrease in the static pressure acting on such fan resulted in an increase in the speed of the fan and the electric motor driving it. Conversely, if the static pressure acting on the fan was increased, the speed of the fan and the electric motor decreased. Thus, the speed of the fans and electric motors utilized in the past systems varied inversely, i.e., in an inverse relation, with a variation of the static pressure in the past system.
While blowers of the squirrel cage type have also been employed in the past systems, the Applicant has ascertained that a decrease in the static pressure acting on such squirrel cage blower results in a decrease in the speed of the squirrel cage blower and the electric motor driving it. Conversely, Applicant has also ascertained that if the static pressure acting on the squirrel cage blower is increased, the speed of the squirrel cage blower and its driving electric motor is increased. Thus, it was found that the speed of the squirrel cage blower and its driving electric motor varies directly, i.e. in following relation, with a variation of the static pressure.